Among the many possibilities for increasing the efficiency of the conversion of coal or other fossil fuels into electric power is open-cycle magnetohydrodynamic power generation (MHD). A typical open-cycle MHD system includes a combustor for generating a high velocity stream of high temperature, ionized gaseous products and a generating channel through which the high temperature gas mixture passes while being subjected to a strong magnetic field. The swift passage of the gaseous ions transversely through the magnetic field induces a flow of current in the gas which may be tapped by means of electrodes in the channel walls. Conversion efficiencies of 90% or better are theoretically possible in such an arrangement.
As the inducement of current flow is dependent upon the degree of ionization in the high temperature gas mixture, most proposed MHD systems specify the addition of a chemical "seed" such as potassium carbonate or potassium sulfate which functions to lower the mixture ionization temperature and thus augmenting the degree of ionization. Typical channel exit gas temperatures are in the range of 3800.degree. to 3600.degree. F. (2093.degree. to 1982.degree. C). As the amount of heat energy in the exiting gas mixture is still quite large, a heat recovery furnace is utilized downstream of the generating channel to recover the heat present in the gas mixture and to convert that heat into high pressure steam for use in driving a generating steam turbine.
Economic studies have shown that in order to successfully compete with less efficient, but simpler, power plant cycles utilizing coal as a fuel, an open cycle MHD generating station must effectively recycle the potassium seed material. There is currently a technological need for a waste heat recovery system that will facilitate condensation and recovery of the potassium seed compounds in a form which is amenable to recycling the recovered compounds to the high temperature coal combustor.